Efficiency optimized hybrid operation strategy

Abstract

A propulsion system for a fuel cell hybrid vehicle that includes a fuel cell system and an EESS, where the propulsion system employs an algorithm for increasing system efficiency. A power limit value is defined as the maximum system efficiency times the charge/discharge efficiency of the EESS. If the vehicle operator requests a power greater than the power limit value, then the fuel cell system will preferably provide the power, and if the power request from the vehicle operator is less than the power limit value, then the EESS will preferably provide the power. The algorithm also considers changing operation conditions and parameters that impact the fuel cell system efficiency and the electric energy storage system efficiency, such as the state of charge of the EESS and regenerative braking.

Description

BACKGROUND OF THE INVENTION[0001]1. Field of the Invention[0002]This invention relates generally to a fuel cell hybrid vehicle with a propulsion system that employs an algorithm for efficiently determining a distributed power draw from a fuel cell system (FCS) and an electric energy storage system (EESS) and, more particularly, to a fuel cell hybrid vehicle that employs an algorithm for efficiently determining the distributed power draw from an FCS and an EESS by defining a power limit value and using EESS power if a power request is below the power limit value and using fuel cell system power if the power request is above the power limit value.[0003]2. Discussion of the Related Art[0004]Hydrogen is a very attractive fuel because it is clean and can be used to efficiently produce electricity in a fuel cell. A hydrogen fuel cell is an electro-chemical device that includes an anode and a cathode with an electrolyte there between. The anode receives hydrogen gas and the cathode receive...

AI Technical Summary

Benefits of technology

[0012]In accordance with the teachings of the present invention, a propulsion system for a fuel cell hybrid vehicle is disclosed that includes a fuel cell system (FCS) and an electric energy storage system (EESS), where the propulsion system employs an algorithm for increasing system efficiency. A power limit value is defined considering the maximum FCS efficiency and the efficiency of the EESS. If the vehicle operator requests a power greater than the power limit value, then the fuel cell system will provide the power, and if the power request from the vehicle operator is less than the power limit value, then the EESS will provide the power. The algorithm also considers changing operation conditions and parameters that impact the fuel cell system efficiency and the electric energy storage system efficiency, such as the state of charge of the EESS and regenerative braking.

Problems solved by technology

MEAs are relatively expensive to manufacture and require certain conditions for effective operation.

The dynamic power of a fuel cell system for a vehicle is limited.

Further, the time delay from system start-up to driveability and low acceleration of the vehicle may not be acceptable.

The voltage cycles can decrease the stack durability.

However, vehicle acceleration may require 100 kW or more of power.

The size of the EESS is an important design consideration for the vehicle propulsion system, which is influenced and limited by cost, weight and performance requirements.

If the SOC of the EESS does not allow for the discharge, the hybrid power system is only able to provide the maximum power from the fuel cell system.

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